1. Field of the Invention
The invention generally relates to electrical lead-throughs, in particular for conducting electrical currents to and from hermetically sealed tanks. The invention especially relates to the outer side insulation of the one or more conductors of such a lead-through.
2. Description of Related Art
Electrical lead-throughs are used, among other things, as component parts or mounted parts of hermetically sealed tanks in order to conduct currents and electrical signals to and from such tanks. Vacuum tanks, in which electrical currents must be conducted into the inside of the tank, can be named as an example. Among other conditions, if high temperatures can occur on the lead-through, plastic is no longer sufficient as insulation for the conductor. Also, in the case of lead-throughs for vacuum applications, many times a very low permeability of the insulation material is required. With these prerequisites, plastic is generally unsuitable as an insulation material for the conductor. High requirements are also placed on electrical lead-throughs of safety tanks. Such tanks can be hazardous goods tanks or, in particular, tanks used in nuclear engineering, such as, e.g., reactor chambers. Here also, the lead-through should have a permeability that is as small as possible in order to prevent the penetration of hazardous materials in or out. In addition, such a lead-through also must be able to withstand high temperatures for a long time. In particular, in the case of safety tanks used in nuclear engineering, here also the long-term stability of such a lead-through is decisive for operational safety. Glass has proven particularly suitable as an insulation material for such applications. Problems may still occur, however, on the conductors themselves. For example, metal conductors are at risk of corrosion. Such a lead-through should also still function in moist environments. For example, if steam is formed inside or outside of the safety tank and moisture condenses on the conductors, the occurrence of leakage currents should be avoided.
Shrink tubings have previously been utilized for the purpose of insulating conductors of lead-throughs for safety tanks. In this case, the conductors have been tightly ensheathed in a water-tight manner by heat shrinkage. The preferred material for these tubings has previously been polyolefin. Such shrinkage tubings, however, have several disadvantages. In order to obtain sufficient flame resistance, such shrinkage tubings are in general treated with flame retardants. These flame retardants that usually contain halogens, however, are toxic and thus are not suitable for all applications. Also, shrinkage tubings are comparatively more expensive as an insulation material.
It would thus be desirable to improve electrical lead-throughs with respect to the above-named disadvantages.